In this program a 3 angstrom unit resolution Scanning Transmission Electron Microscope (STEM) with a -170 degrees C cold stage will be used to image biological molecules with minimum possible degradation by radiation damage. Frozen hydrated preparation will be used to minimize structural change of the specimen when inserted into the microscope ultra-high vacuum. These images will supplement structural data obtained by x-ray and neutron diffraction studies. The STEM facility will be jointly used by the Brookhaven scientific staff and by academic scientists as a Biotechnology Resource. The ability of the STEM to image unstained molecules and to localize single heavy atoms within an organic matrix will be used to locate heavy atom binding sites of biological molecules. The quantitative relationship between electron scattering properties and specimen composition will be used to relate the detected scattering properties and specimen composition will be used to relate the detected scattering to molecular weight of the imaged molecule. Initial studies have begun on nucleic acids (DNA), virus particles, enzyme complexes and structural molecules such as the components of muscle and cell membrane. Studies of thicker specimens such as chromosomes are also in progress.